Eric Schmidt, the executive chairman of Google, has called them the "gang of four." They are the four titans of tech: Google, Apple, Facebook and Amazon. Four titans of tech

Eric Schmidt, the executive chairman of Google, has called them the "gang of four." They are the four titans of tech: Google, Apple, Facebook and Amazon. And they are impossible to escape, tapping nearly every consumers' wallets and holding vast power over huge swathes of the economy.

The companies are racing one another to be king of the digital age, and each is lacking something that another has. Put in the missing pieces, and one company has the potential to be all things to all people - a complete system in which consumers spend most of their time watching videos, reading, writing and making purchases.

"It's the biggest, most intense battle in tech history," said Ted Morgan, chief executive of Skyhook Wireless, a firm that provides location-based technology for mobile devices. "It's so much bigger than even the Microsoft, Apple, IBM battles of the 1990s. I think all four of those guys know it's between us four."

Google's announcement on Monday that it will acquire cell phone-maker Motorola Mobility Holdings, is a move that will send it even further into Apple's smartphone turf.

Google, with its powerful search algorithm, has made money by selling ads that appear alongside its search results. Instead of manufacturing its own devices, the company offered its Android software to run on phones built by others, including Motorola, Samsung and HTC.

Whereas, Apple has built its success by selling computers, phones and tablets that work seamlessly with the company's software programs. "Apple is basically an ecosystem with end-to-end delivery," said Michael Gartenberg, an analyst at Gartner. The two firms weren't always such fierce rivals.

Facebook founder Mark Zuckerberg's ambitions are grander - and they run directly into those of the three other titans. Facebook hopes to be an alternative way to organise the Web, a platform for consumers to spend their time online.

Amazon, the world's biggest online retailer, is benefiting from growing sales of its Kindle e-book reader and digital media, including books, movies and music, putting it in competition with Apple's iTunes. Apple, Amazon and Google have a combined market capitalisation of $616 billion. Facebook plans to go public soon.